I really don't see the harm in what he posted on Twitter.
People should stop lashing out at every little thing. There's nothing fundamentally wrong with a little tease every now and then. So take it for what it's worth, and get excited that Affleck is going full throttle into his workout. Or there's always the option of going back to total radio silence from everybody involved in this production, since that's been such a wonderful experience the last few months